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					Medical Equipment




                    1
 Required Text Books and References


Hand Book of Biomedical Instrumentation,
R. S Khandpur
Introduction to biomedical equipment technology,
J. J. Carr; J. M. Brown
Medical Instrumentation, J. G. Webster




                                              2
                Introduction

1. What is a medical instrument
2. Medical Instruments Classes




                                  3
     What is a Medical Instrument
A ‘Medical Instrument’ is any instrument,
apparatus, appliance, material or other article,
whether used alone or in combination, including
the software necessary for its proper application
intended by the manufacturer to be used for
human beings for the purpose of:
  diagnosis, prevention, monitoring, treatment or
  alleviation of disease,
  diagnosis, monitoring, treatment, alleviation of or
  compensation for an injury or handicap,
  investigation, replacement or modification of the
  anatomy or of a physiological process,
  control of conception, and which does not achieve its
  principal intended action in or on the human body by
  pharmacological, immunological or metabolic means,
  but which may be assisted in its function by such
  means
                                                      4
       Medical Instruments Classes
Class I: General Controls: devices present minimal
potential for harm to the user and are often simpler
in design than Class II or Class III devices such:
  tongue depressors, bedpans, elastic bandages,
  examination gloves, and hand-held surgical instruments
  and other similar types of common equipment, …..etc
Class II: General Controls with Special Controls :
are those for which general controls alone are
insufficient to assure safety and effectiveness.
They are typically non-invasive and include:
  x-ray machines, PACS, powered wheelchairs, infusion
  pumps, surgical drapes, surgical needles and suture
  material, and Acupuncture needles,………etc
                                                      5
  Medical Instruments Classes (cont.)
Class III: General Controls and Premarket
Approval : device is one for which insufficient
information exists to assure safety and
effectiveness solely through the general or special
controls sufficient for Class I or Class II devices.
Such a device needs premarket approval, a
scientific review to ensure the device's safety and
effectiveness. They are life-supporting or life-
sustaining devices such:
  replacement heart valves, silicone gel-filled breast
  implants, implanted cerebral stimulators, Ventilators,
  bed side monitors, ….etc

                                                      6
               1. X-Ray Systems
1-1. Fundamentals of X-Ray
     Production of X-Rays
     Properties of X-Rays
     Units of X-Radiation
1-2. X-Ray Machine
     X-Ray Generator:
       High Voltage generation
       High frequency generation
       Automatic Exposure Control
     X-Ray tube
     High tension cable
     Collimators and Grids

                                    7
           1. X-Ray Systems (Cont.)
1-3. Visualization of X-Rays
    X-Ray Films
    Fluorescent Screens
    X-Ray Image Intensifier Television System
1-4. Examination Table
1-5. Kinds of X-Ray Machines
    Mobile Unit
    Dental Unit
    Mammography Unit
1-6. Digital Radiography
    Overview

                                                8
        1-1. Fundamentals of X-Ray
Production of X-Rays:
  X-rays (or Röntgen rays) are a form of electromagnetic
  radiation with a wavelength in the range of 0.01 to 10
  nanometers, corresponding to frequencies in the range
  30 to 30 000 PHz (1 PHz = 1015 Hertz)
  X-rays are produced whenever electrons collide at very
  high speed with matter and are thus stopped
  The energy possessed by the electrons appears after
  collision in two forms:
     99 % Heat
     1 % X-rays



                                                      9
    1-1. Fundamentals of X-Ray (con.)

Properties of X-Rays
  Short wavelength
  Extremely high energy
  Able to penetrate through materials
  Absorbed when passing through matter
  Extent of absorption depends upon the density
  of matter
  Produce secondary radiation in all matter
  through which they pass


                                            10
     1-1. Fundamentals of X-Ray (con.)

Units of X-Radiation
The measure of the quantity of x-radiation is “Rontgen” (R)
Rontgen is the ability of radiation to produce ionization
One (R) is the amount of x-radiation which will produce
2.08x109 ion pairs per cubic centimeters of air at standard
temperature (0oC) and pressure (760 mmHg) at sea level.
The curie (Ci) is the old standard unit for measuring the
activity of a given radioactive sample.
The Becquerel’s is the more recent SI unit for radioactive
source activity (1 curie = 3.7 x 1010 Becquerel's)
Rad: Measurement unit of absorbed dose ( SI: Gray)
rem: Measurement unit of the relative biological damage as
results from the absorbed dose (SI: sieverts (Sv) )
                                                        11
    1-1. Fundamentals of X-Ray (con.)
Units of X-Radiation (cont.)




                                        12
               1-2. X-Ray Machine
Generate high-energy, high frequency electromagnetic
waves (X-Rays) for use in diagnostic and treating disease
Block diagram of an x-ray machine




                                                     13
                X-Ray Generation

X-Ray Generator
  High     voltage    generator:
  modifies incoming voltage and
  current to provide an x-ray
  tube with the power needed to
  produce an x-ray beam of the
  desired peak kilovoltage (kVp)
  and current (mA) and duration
  (Time).
  Major components are:
    Control panel
    Transformer assembly
                                   X-ray generator components

                                                            14
                X-Ray Generation

Control panel
  Permits the selection of
  technique factors and
  initiation of radiographic
  exposures
     mA, kV, Time
Transformer assembly:
  Transformer
  Rectifiers
  Three major circuits:
     High voltage circuit
     The filament circuit
     Timer circuit                 15
              X-Ray Generation

Transformer: Transformers modify the voltage of
incoming alternating-current (AC) electrical
signals to increase or decrease the voltage in a
circuit.
  Step-up transformer supplies the high voltage to the
  x-ray tube (voltage increases and current decreases)
  Step-down transformer supplies power to heat the
  filament of the x-ray tube (voltage decreases and
  current increases)
  Autotransformer: Supplies the voltage for the two
  circuits and provide a location for the kVp meter
  (indicates the voltage applied across the x-ray tube)
                                                     16
                X-Ray Generation
Rectifiers: convert AC into the direct current
(DC) required by the x-ray tube.
A rectifier restricts current flow in an x-ray tube
to one direction (from cathode to anode),
thereby preventing damage to the x-ray tube
filament.
Two types:
  Half wave
  Full wave



    Voltage waveforms rectification
                                                 17
                    X-Ray Generation
Depending on the rectifiers and components
included in the high-voltage circuit, the voltage
waveform presented to the x-ray tube can be:
  Ideal DC
  Single phase half wave
  Full-wave rectified




  Voltage x-ray tube waveforms
   (left) and radiation intensity
          waveform (right)


                                              18
                 X-Ray Generation
3-phase, 6 pulses
3-phase, 12 pulses
High frequency
Constant potential




Voltage x-ray tube waveforms
 (left) and radiation intensity
        waveform (right)



                                    19
                   X-Ray Generation




Single phase full waveform
      rectified circuit

                             Three phase full wave rectifier



                                                           20

				
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